1. Field of the Invention
The present invention relates to a plasma display panel capable of color displaying, particularly to a plasma display panel which can perform color displaying and allow an improved visibility.
The present application claims priority from Japanese Application No. 2001-111228, the disclosure of which is incorporated herein by reference for all purposes.
2. Description of the Related Prior Art
A plasma display panel comprises a pair of glass substrates facing each other and having an electric discharge space formed therebetween. The pair of glass substrates include a front glass substrate providing a display surface and a rear glass substrate positioned opposite to the front substrate. In fact, such a plasma display panel is an AC-type display panel, the front substrate of which has a plurality of row electrode pairs formed by transparent electrodes (for electric discharge) and provided on the inner surface of the front substrate. Actually, these row electrodes are covered by a transparent dielectric layer as well as a protection layer. On the other hand, the rear glass substrate has a plurality of column electrodes serving as data electrodes (for data writing) and provided on the inner surface thereof. Similarly, these column electrodes are covered by a protection layer.
The front glass substrate and the rear glass substrate are bonded together along their edge portions with a sealing layer interposed therebetween. In fact, between the front glass substrate and the rear glass substrate, there are provided a plurality of stripe-like partition walls forming a plurality of elongated discharge spaces along the column electrodes. In this way, the row electrodes are arranged to be orthogonal to the column electrodes. Further, each elongated discharge space is provided with a fluorescent layer for emitting a visible light or for producing a color effect and is filled with a discharge gas which is in fact a gas mixture mainly containing neon gas and xenon gas. In practice, the fluorescent layers include three original colors Red, Green and Blue which are arranged in a predetermined regular order, thereby effecting a desired color display.
In use, an electric discharge is selectively effected in accordance with display data, along each display line formed by a pair of row electrodes. In fact, such discharge is effected between one of the two electrodes forming the row electrode pair and a column electrode. Accordingly, lighting cells (having wall charges formed therein) and erasing cells (not having wall charges formed therein) are thus selectively formed, thereby forming a desired picture on the display. Then, a plurality of sustaining pulses are repeatedly supplied to the display lines, so as to maintain the light emission of the lighting cells by applying the sustaining pulses.
However, the above-described conventional plasma display panel has at least the following problems caused due to contrast drop which is in turn caused due to an external light reflection.
Namely, since fluorescent material used in the plasma display panel is formed by an inorganic fluorescent powder, there is a large reflection caused due to external light reflection. As a result, erasing cells serving as non-displaying portions will be recognized brightly due to the external light reflection, making it impossible for the non-displaying portions to produce sufficient black display.
Another problem associated with the above-described conventional plasma display panel is caused due to a visible light emitted by the neon gas contained in the discharge gas. Namely, when the discharge gas mainly contains the neon gas and xenon gas, an ultraviolet light emitted during an electric discharge can cause the excitation of the respective fluorescent layers, thereby emitting visible light rays having spectral characteristics corresponding to the respective fluorescent layers. At this time, the neon gas itself emits a light which is a visible light ray having a peak in a specific wavelength region. In fact, the neon emission will cause neon light component (having an emission peak in the vicinity of about 590 nm) to occur in the light emission spectrums of the respective color light rays, thus reducing the color purity of the respective color light rays and causing a low contrast for the plasma display panel.
In order to avoid the low contrast of a plasma display panel (which is caused due to external light reflection), an absorption type ND filter having a substantially uniform transmittance everywhere is provided on the displaying side of the plasma display panel. Alternatively, a color filter corresponding to the respective fluorescent layers of R,G,B colors is disposed at the same position in order to obtain the similar effect. However, in the case where ND type filter is used, although an external light reflection can be reduced and thus the contrast of the plasma display panel is improved, it is difficult to avoid a significant reduction in the brightness of the display panel (if it is desired to avoid undesired effects caused by the external light reflection as well as by the neon emission). On the other hand, in the case where the color filter is employed, production cost will be increased due to the use of a color filter capable of handling various colors.
An object of the present invention is to provide an improved plasma display panel capable of effectively inhibiting a contrast drop possibly caused due to neon light emission, thereby ensuring an improved contrast and an improved color purity while at the same time minimizing the brightness drop of the display.
In a first aspect of the present invention, there is provided a plasma display panel comprising: a pair of substrates arranged opposite to each other with an electric discharge space formed therebetween; an amount of electric discharge gas mainly containing neon and xenon, which is sealed within the electric discharge space; and a plurality of fluorescent layers disposed within the discharge space, which fluorescent layers are adapted to be excited by an ultraviolet ray emitted from the discharge gas, so as to emit light rays of red, green and blue colors.
In particular, an optical filter is provided on the front side of the display panel, said optical filter having such an transmission characteristic that the filter can selectively attenuate light components having a wavelength range extending from the wavelength region of a visible light emitted by neon gas to a longer wavelength region which is close to a wavelength at which an emission characteristic of each green-light emitting fluorescent layer exhibits its peak.
In a second aspect of the invention, the light components to be selectively attenuated by the optical filter have a wavelength of 560-590 nm.
In a third aspect of the invention, the optical filter is so formed that its transmittance for light components to be selectively attenuated is 70% or less of its transmittance corresponding to a wavelength at which the emission characteristic of red light emitting fluorescent layer exhibits its peak.
In a fourth aspect of the invention, the optical filter is so formed that its transmittance for light components to be selectively attenuated is 80% or less of its transmittance corresponding to a wavelength at which the emission characteristic of green light emitting fluorescent layer exhibits its peak.
In a fifth aspect of the invention, the optical filter is so formed that its transmittance for light components to be selectively attenuated is 70% or less of its transmittance corresponding to a wavelength at which the emission characteristic of blue light emitting fluorescent layer exhibits its peak.
According to the first aspect of the present invention, with the use of the optical filter provided on the front side of the plasma display panel, it becomes possible to selectively attenuate light components having a wavelength range extending from a wavelength region of a visible light emitted by neon gas to a longer wavelength region which is close to a wavelength at which an emission characteristic of each green-light emission fluorescent layer exhibits its peak. In this way, it is possible to attenuate a neon emission peak on a longer wavelength side when a blue light emitting fluorescent layer or a green light emitting fluorescent layer acts as a light emitting section, it is also possible to attenuate a neon emission peak on a shorter wavelength side when a red light emitting fluorescent layer acts as a light emitting section, thereby making it possible to clearly divide spectrum characteristics of various colors and thus improve color purity. In fact, light components (having a wavelength range extending from a wavelength region of a visible light emitted by neon gas to a longer wavelength region which is close to a wavelength at which an emission characteristic of each green-light emitting fluorescent layer exhibits its peak) contain peaks of spectral characteristics of while color fluorescent lamps commonly used in indoor illumination. Further, since these light components are in a wavelength region having a high specific visibility, the selective attenuation is effective for attenuating an external light reflection of the plasma display panel (caused due to indoor illumination), thereby effectively preventing the contrast drop possibly caused due to the external light reflection. Moreover, since it is possible to set a sufficiently high transmittance for other light components having other wavelengths than those described in the above, the use of the optical filter makes it possible to effectively minimize the brightness drop.
According to the second aspect of the invention, light components to be selectively attenuated by the optical filter has a wavelength of 560-590 nm. Namely, a neon emission peak occurring in the vicinity of 590 nm is attenuated, and it is possible for an attenuation effect to extend to a wavelength region in the vicinity of 530 nm which is a peak wavelength representing an emission characteristic of each green light emitting fluorescent layer. In this way, it is possible to inhibit an orange light emission produced by each red light emitting fluorescent layer, as well as to inhibit yellow/green light components emitted by each green light emitting fluorescent layer and blue light emitting fluorescent layer, thereby improving the color purity of the fluorescent layers of various colors R, G, B. Further, since the light components in the wavelength region of 560-590 nm are attenuated from external light reflection at non-light emitting sections, it is possible to effectively reduce the external light reflection caused due to indoor illumination containing light components having such a wavelength.
According to the third to fifth aspects of the invention, the optical filter is so formed that it exhibits a transmittance which is 70% or less of the transmittance of a red light, 80% or less of the transmittance of a green light, 70% or less of the transmittance of a blue light, thereby ensuring a sufficient transmittance for each light component and thus minimizing a brightness drop.